1. Field of the Invention
This invention relates to a unique process for extracting and recovering aluminum from aluminum-containing raw materials, including low-grade ores, by contacting said ores with an aluminum-organo complex-forming reagent at a temperature up to 150.degree. C for a predetermined period of time.
2. Description of the Prior Art
As the domestic demand for aluminum metal continually increases at a greater rate than the supply, new and improved technology for mineral processing must be developed to increase the production of aluminum. Aluminum has been extracted and recovered commercially for 86 years by the Bayer process, which is actually applicable only to high quality bauxite ores. Despite recent modifications of the Bayer process, it still presents several shortcomings.
First, the process is only capable of extracting aluminum from hydrated aluminum oxide ore minerals, such as gibbsite and boehmite, but it is incapable of recovering aluminum from other types of potential ores such as anorthosite and clays. Therefore, aluminum in kaolins which are frequently associated with bauxites, or aluminum present in goethite is not extractable under the digestion conditions of the Bayer process. For example, in highly bauxitic goethite, the unextractable alumina is often found to be as high as 5%, by weight, of the bauxite.
Second, bauxites containing an excess of 5% silica in other minerals are not considered suitable for direct processing by the Bayer method, because of the high cost of removing silica in digestion so as to prevent contamination in the aluminum production. Third, the simultaneous presence of boehmite and gibbsite in most ores always poses a problem in controlling the digestion conditions of the process to better recover aluminum from the mixture of both these minerals.
Fourth, the presence of very fine particle sizes of the bauxite and the resulting red mud (iron oxides, titania and silica) makes it difficult to efficiently separate the red mud from the caustic aluminate liquor. Although a floculation-decanting technique may be used for this separation, the high content of organic matter in certain bauxites inhibits floculation of the red mud, and hence contaminates process liquors. Finally, the disposal of red muds in alumina production is a well-recognized environmental problem facing the processing plants. These and other related problems in the Bayer process point out a need for new technology of extraction and separation in order to economically utilize all bauxite materials and other aluminum-containing raw materials.
That is to say, such a new and improved technology should not only recover aluminum more efficiently from bauxite materials -- 95% of which are imported in the United States -- than the current Bayer process, but also should be applicable to the extraction of aluminum from low-grade ores such as anorthosite, alunite and clays which are abundant.